In an image forming apparatus, such as a copying apparatus, an intermediate tray is provided inside the apparatus and an image is formed on both sides of sheets by using the intermediate tray. In this image forming apparatus, after a sheet where the image forming process on one side is completed is temporarily stored in the intermediate tray, the sheet is again carried to an image forming section so that an image is formed on the other side of the sheet. Besides such an apparatus, there also exists an image forming apparatus having a post-processing unit, such as a stapler for stapling a plurality of sheets where images have been formed on one side or both sides.
The intermediate tray and the stapler, which are used for such a double-sided image forming process, requires common processes, such as a sheet adjusting process, a process for stacking a plurality of sheets. In this case, when the intermediate tray and the stapler are individually attached to the image forming apparatus as separate units, mechanisms for common processes are duplicated. As a result, the apparatus becomes large and the number of parts increases, thereby causing a rise in costs.